1. Field of the Invention
The present invention relates to epidural catheters and, more particularly, to biocompatible, biodegradable epidural catheters suitable for use in a continuous epidural anethesia procedure comprising a synthetic absorbable polymer.
2. Description of the Prior Art
Epidural blockade has become popular among anesthesiologists and surgeons since it does not entail the risks associated with general anesthesis and can be used to provide complete anesthesia during a prolonged surgical operation. The epidural procedure involves the administration of an anesthetic agent in sufficient dosage into the epidural space to affect all modalities of nerve function, including sensory, motor, and autonomic impulses. To provide a continuous epidural block for the duration of surgery and, if required, into the postoperative period, a flexible, plastic epidural catheter is normally introduced so that repeated or continual injections of an anesthetic agent can be made.
While the insertion of the catheter during the epidural procedure is usually safe, conventional epidural catheters manufactured from non-irritating, flexible plastic materials such as polymers of tetrafluoroethylene, have been knoen to break during removal, leaving a segment lodged in the patient's back. Due to the increased risk to the patient, surgical removal of a broken catheter is not recommended and since the severed nonbiodegradable catheter is located in an anatomical region which does not permit it to be naturally extruded, it must be left in the patient permanently. In any event, the discomfort to the patient and the formidable complications that may likely result from such a mishap following or during the epidural anesthesia procedure could greatly deter surgeons, anesthetists and patients from this most useful anesthetic technique.
To avoid the disadvantages associated with nonbiodegradable delivery systems, a number of biodegradable materials have been used or proposed in the prior art for the manufacture of medical devices based upon ingestion, injection, vaginal and uterine insertion, percutaneous application and subcutaneous implantation. Such absorbable materials as natural collagens, commonly known as catgut, hydrogels, gelatin, methyl cellulose, and polyvinyl alcohol derivatives have traditionally been suggested for these purposes as described in U.S. Pat. Nos. 2,072,303, 2,593,980 and 3,358,684. However, those materials, such as methyl cellulose and polyvinyl alcohol, which are water-soluble are unsatisfactory for use as epidural catheters because it is not possible to control their rate of absorption by living tissue over any appreciable length of time and, therefore, these materials become dimensionally unstable in the body. Also, those materials, such as hydrogels, gelatin and collagens, which are water-swellable do not maintain their structural integrity within the body and there appears to be no satisfactory continuous method for fabricating these materials into fine tubes which would facilitate their use as epidural catheters. Moreover, the absorption process of a natural collagenous material takes place in the body through enzymatic degradation which may result in adverse cellular infiltration and irritation.
More recently, it has been proposed to manufacture sutures, prosthetic devices, implantable drug delivery systems, surgical drainage or testing tubes and tubular structures having use in the surgical repair of arteries, veins and the like from synthetic absorbable polymers such as polylactide, polyglycolide, copolymers of lactide and glycolide, and polydioxanone. Such polymeric articles are described in U.S. Pat. Nos. 3,297,033; 3,463,158; 3,636,956; 3,736,646; 4,052,988; 4,650,488; 4,697,575; 4,706,652 and elsewhere in the literature. However, none of these references suggest a biodegradable catheter made of synthetic polymers of absorbable materials for use in an epidural anesthesia procedure in accordance with a primary object of the present invention.